Full agonists
A full agonist is a ligand that binds to a receptor and produces the maximal possible biological response for that receptor system (maximal efficacy).
Key pharmacology features
- Full agonists have high efficacy and can drive the response to the receptor’s maximum level under saturating conditions.
- Full agonists differ from partial agonists, which elicit a less-than-maximal response even at full receptor occupancy.
- Full agonists differ from antagonists, which do not produce a receptor-mediated response and instead block receptor activation.
Clinical relevance
- Full agonists can produce dose-dependent increases in effect up to the maximum receptor response, which is clinically expressed as maximal pharmacologic efficacy.
- In mixed receptor settings, a full agonist can displace a partial agonist and increase effect toward maximal response because the full agonist has higher efficacy.
Examples
- Morphine is a full agonist at the mu-opioid receptor.
- Fentanyl is a full agonist at the mu-opioid receptor.
Distinguishing from receptor affinity
- Full agonism refers to efficacy (response capacity) rather than receptor affinity (binding strength).
- A ligand can have high affinity without being a full agonist if its maximal effect is limited.